The acoustic hollow-body guitar, herein referred to as the ‘guitar’, in its various forms is among the most popular of musical instruments in use today and is central to a multitude of traditional and contemporary musical genres. As such, the guitar has evolved, and continues to evolve, both in response to changing musical styles and needs, and in response to a maturing appreciation of its subtler tonal and expressive qualities and the possibilities for further development in this regard.
The particular sound or ‘voice’ of an individual guitar derives from its overall design, materials and construction. The sound that we hear is the result of the plucked strings' patterned energy being filtered through the guitar's unique combination of physical attributes, resulting in complex behaviors of its planar surfaces and enclosed air volume, which produce patterned compression waves in the instrument's immediate atmosphere. These waves, traveling through the air to excite our eardrums as impulses which register as sound in our brain, represent more or less of the strings' original energetic activity. The amount and harmonic depth of the original string signal that is manifest in audible form is a basic measure of a guitar's acoustic quality.
The driven and sympathetic activity of the guitar's compliant top and back plates, and of its enclosed air chamber, serve to ‘amplify’ the otherwise inaudible energy of the vibrating strings and to enhance that signal with their natural resonances. To the degree that the resonances of these three active components are both strong and tuned to intended frequencies, the potential exists for an instrument of exceptional power and tonal quality. Unfortunately, some basic elements of conventional guitar design make the manipulation and control of the guitar's main resonances extremely difficult if not literally impossible. An approach to guitar construction that allows for and facilitates adjusting the amplitudes and center frequencies of the instrument's main resonances represents an advance of the guitar makers' art.
The various concurrent ‘dimensions’ of the guitar—its acoustical, structural, functional, and aesthetic realms—are inseparably linked as a coupled system throughout, making the manipulation of any single variable in isolation from the rest of it, all but impossible. The intimately bound and often antagonistic relationship between the guitar's acoustical and structural functions is well known to experienced guitar makers. Actions at the workbench which are intended to optimize either one of these primary and equally important aspects of the guitar can simultaneously compromise the other aspects in ways often unanticipated by builders with limited experience in, and knowledge of the craft. Understanding and balancing the often contradictory requirements of acoustical brilliance on the one hand and structural soundness on the other is one of the guitar maker's most fundamental and constant challenges, the resolution of which is often ultimately frustrated by limitations that are inherent in standard guitar construction practices. The need to overcome or to at least extend those limitations requires a reexamination of standard construction conventions and inspires the present alternative, less limiting approach to some of the craft's more problematic design issues.
The present invention relates to a steel string acoustic guitar that achieves both its desirable tonal qualities and its exceptional structural integrity through the incorporation of unique construction design elements in the guitar's body—particularly from the use of domed, composite, low-mass honeycomb-core top (soundboard) and back plates, each with adjustable (variable stiffness) tone bars, along with a composite, relatively thick-walled, rigid rim which functions as an independent superstructure to which the guitar's aforementioned top and back plates, and its neck, are separately attached.
Because a plucked string's energy is finite—limited and short-lived—the efficiency and completeness with which that energy is converted into sound is a basic measure of a guitar's usefulness and value as a musical instrument. One approach to harvesting as much as possible of the strings' energy for sound is to minimize the amount of that energy that is required to move the weight of the soundboard. Lower mass—less soundboard weight—generally correlates to greater soundboard efficiency. Beyond preserving precious string energy, a lighter, more sensitive soundboard can potentially respond to and make audible more of the strings' finer/higher harmonic content, further enriching the character of the instrument's musical voice.
With less mass needing to be set into motion before each note can be realized, a lighter soundboard can also deliver a quicker, more immediate response to the player's fingers' attack. By contrast, many otherwise fine sounding guitars have a “speed limit”, notes played faster than which lose their crisp separation and seem to overlap in an aural “jumble”. A guitar with the shortest, most immediate response time—a guitar that cannot be over run by the fastest finger work—is an especially desirable quality in today's world of virtuoso guitar players.
Typical sets of six steel strings pull on the soundboard with approximately 140 to 200 pounds of tension. Because the conventional solid wood soundboard plate, made thin and light enough to be driven efficiently by the strings, is, by itself, too easily distorted and pulled up above its proper height by the pull of the strings, prior art installs stiff wooden longitudinal braces on the underside of the soundboard plate to maintain the plate's intended contour and orientation. While accomplishing their stabilizing purpose, these structural members impose on the soundboard more or less arbitrary patterns of stiffness that lie across antinodes of the plate's various natural resonance modes, inhibiting and/or essentially eliminating them from the plate's potentially complete set of stacked natural resonances. This creates “holes” or gaps in the guitar's frequency output response, an unintended filtering about which little can be done in the context of conventional construction.
The composite, domed, low-mass ‘torsion box’ structure of the soundboard plate of the present invention, while lighter in weight than its conventional solid wood equivalent, is strong enough to resist distorting in response to the pull of the strings, without the use of conventional braces in the critical lower bout—the region of the soundboard's main diaphragm. Thus, unrestricted to a significant degree in its responses to the strings' energy input, and more uniform in its directional stiffness, the soundboard of the present invention is free to realize the entire range of its natural resonances more fully than in a conventional soundboard. The resulting more complete frequency output can be heard clearly as what has anecdotally been called “more piano-like” in describing its fullness of tonal content, and it can be clearly seen, when charted by spectral analysis instrumentation, as maintaining an unusually consistent output level across its frequency range, without the typically deep, irregular gaps that characterize the charted output levels of conventionally constructed guitars.
While the above discussion is focused on the nature and activity of the directly driven soundboard, much the same can be said of the guitar's back plate, which is driven less directly by the activity of the soundboard, and principally through the enclosed air volume's patterned changes in pressure. The back plate of the present invention enjoys the same freedom from the conventional braces and the effects of their overlaid patterns of stiffness. The basic stiffness of the present back plate can be varied in it's laminated construction, casting it as a more rigid energy reflector or conversely as a more compliant secondary resonator and radiator.
In a similar but different lamination scheme, the guitar rim (the “sides”) of the present invention has been made thicker and stronger, thereby eliminating both the need for side structural braces and the gluing surface offered by its broad cross-section. This in turn, eliminates the need for the perimeter linings that are required to join top and back plates to the conventionally thin, narrow edged rim. The natural resonance frequencies of the resulting thicker and relatively rigid rim are raised well above the compass of the instrument, essentially eliminating the potentially negative effects of the conventional thin-walled rim as an uncontrolled energy sink.
Freed from the arbitrary and potentially counter-productive restrictions imposed by conventional structural braces, certain aspects of the behavior of the soundboard and back plates of the present invention, such as their fundamental resonance frequencies and their overall relative stiffness, can now be brought under some control through the use of light weight-adjustable (variable stiffness) tone bars, strategically placed with regard to each plate's natural resonance modes. Beyond their role in establishing the desired resonant ‘mix’ in the new guitar's original setup, these adjustable tone bars can be used through the life of the instrument to maintain critical resonance relationships that might otherwise drift out of synch through the effects of either age or seasonal shifts in temperature and humidity. In addition to using the adjustable tone bars to optimize tonal quality in response to changing circumstances, these new devices can also be used to vary the instrument's ‘voice’ to suit the taste of its player.
This new invention utilizes and combines both known and new technologies in a unique and novel configuration to overcome the aforementioned problems of the prior art.